Blast-radius isolation gap: AdminAuth called ValidateAnyToken which
accepted any live workspace bearer token. A compromised workspace agent
could present its own token to GET /admin/github-installation-token and
steal the platform's GitHub App credential, or hit /approvals/pending to
enumerate cross-workspace approvals.
Fix: introduce a dedicated admin credential tier via ADMIN_TOKEN env var.
When set, AdminAuth verifies the bearer against that secret exclusively
(crypto/subtle constant-time comparison). Workspace tokens are rejected
outright — no DB lookup occurs. When ADMIN_TOKEN is not set the previous
behaviour is preserved as a deprecated backward-compat fallback (tier 3)
so existing deployments without the env var don't break immediately.
Credential tiers (evaluated in order):
1. Fail-open — no live tokens globally (fresh install / pre-Phase-30)
2. ADMIN_TOKEN match — env var set, bearer must equal it exactly
3. Fallback (deprecated) — any valid workspace token (ADMIN_TOKEN unset)
Operators should set ADMIN_TOKEN=<openssl rand -base64 32> to fully close
the blast-radius gap. Tier 3 will be removed in a future release.
Fixes#684.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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